Biaxially drawn, blow-molded bottles made of a polyethylene terephthalate resin (hereinafter referred to as PET resin) have had a tendency in recent years in which the bottles are made in a thin-walled configuration. For this reason, the gas barrier property is in much greater demand then ever for these bottles.
In response to this demand, it was proposed to use a co-injection molding method to obtain a primary molding (hereinafter referred to also as preform), which would be molded into a bottle of a laminated structure comprising a PET resin layer, a gas barrier layer, and the other PET resin layer. In another method, the bottles, i.e., the secondary moldings, were given the gas barrier property by blending the PET resin with a gas barrier material, such as nylon (MXD-6), then injection-molding a preform from this blended material, and drawing biaxially and blow-molding this preform into a bottle.
The neck (including the neck ring) of the bottle having the laminated structure used in the former method is a portion that is not drawn, and as such, has a large thickness. At this thickness, the bottle has a full gas barrier property with no special provision of a gas barrier layer. However, in the afore-mentioned conventional art, the gas barrier layer is disposed over the full neck length in the similar way as in the body to prevent the upper end (flow front) of the gas barrier layer from failing to reach the lower end of the neck because of the difference in the height of the gas barrier layer. In that case, the gas barrier material usually exists in the neck portion at a rate of occupancy in the range of 20-40%, and at an average rate of about 30%, in the total amount of gas barrier material to be used for a bottle. A problem arising from this practice is that the gas barrier material used in the neck is wasted and is not effectively utilized.
In the case of a heat-resistant bottle in which the neck is whitened (thermally crystallized), the extent of shrinkage caused by the whitening treatment becomes lower because of a difference in the rate of shrinkage between the PET resin and the gas barrier material if there is a large amount of gas barrier material in the neck. Another problem found in the neck is that after the whitening treatment, the neck tends to have larger dimensions than the set values and an elliptic cross-sectional shape, thus making it difficult to secure the correct settings for the neck.
This invention has been made to solve the above-described problems found in the conventional art. Thus, the technical problem of this invention is to reduce the amount of the gas barrier material laminated in the neck portion as much as possible in the biaxially drawn, blow-molded bottle and preform, in which the PET resin layers are laminated with a gas barrier layer. An object of this invention is to make effective use of the gas barrier material in manufacturing biaxially drawn, blow-molded bottles and preforms of this invention. Another object of this invention is to ensure that the neck of the heat-resistant bottle has the predetermined dimensions after the whitening treatment.
The means of carrying out the invention of claim 1 to solve the above-described technical problems exists in the configurations:
that the preform of the biaxially drawn, blow-molded bottle comprises resinous layers mainly made of polyethylene terephthalate and at least a layer of a gas barrier material laminated with the PET resin layers;
that the gas barrier layer extends downward from a level halfway to the height of the neck including the neck ring, or at least from above the neck ring, down virtually to the lower end of body having the shape of a bottomed cylinder; and
that the gas barrier layer inside the neck wall has an average thickness corresponding to a third (⅓) or less of the maximum thickness of the gas barrier layer inside the body wall.
In the invention of claim 1, the upper end of the gas barrier layer is disposed at a halfway point of the neck or at least above the neck ring. Even if there is some difference in the height of the gas barrier layer at the time of the molding operation, the flow front of the gas barrier layer never fails to reach the lower end of the neck. Therefore, there is no possibility that the gas barrier layer does not exist in the bottle shoulder or upper part of the body of the blow-molded bottle.
The gas barrier layer inside the neck wall extends downward from a level halfway to the neck height, and has an average thickness corresponding to a third (⅓) or less of the maximum thickness of the gas barrier layer inside the body wall. In that case, the amount of the gas barrier material inside the neck wall is far less than the corresponding amount existing inside the body wall. As a result, almost all the gas barrier material is disposed in the body wall. Thus, the gas barrier material can be effectively utilized in this invention.
The means of carrying out the invention of claim 2 exists in the configurations:
that the biaxially drawn, blow-molded bottle comprises resinous layers mainly made of polyethylene terephthalate and at least a layer of the gas barrier material laminated with the PET resin layers;
that the gas barrier layer extends downward from a level halfway to the height of the neck including the neck ring, or at least from above the neck ring, down virtually to a position ranging from the lower end of the body to the bottom; and
that the gas barrier layer inside neck wall has a rate of occupancy of 15% or less in the total weight of the gas barrier material.
In the invention of claim 2, the gas barrier layer inside the wall of the neck of the biaxially drawn, blow-molded bottle has a rate of occupancy of 15% or less in the total weight of the gas barrier material. Even after the bottle has been molded, the amount of the gas barrier material inside the neck wall is far less than the corresponding amount existing in the body wall. As a result, almost all the gas barrier material is retained in the body wall. Thus, the gas barrier material can be effectively utilized in this invention.
In the case of heat-resistant bottle having the neck treated for whitening, the gas barrier layer inside the neck wall has quite a small thickness and is located predominantly in the lower portion of the neck. For these reasons, the gas barrier material does not affect the shrinkage caused by the whitening treatment. Therefore, after the whitening treatment, the neck remains in the predetermined dimensions without fail.